Operator control panels including potentiometers are widely used devices for allowing operator interaction with some type of system which is electronically or computer controlled. One typical application relates to a scene by scene color corrector wherein video parameters of video signals are adjusted. There is often a need in such systems for repetitively controlling certain operational parameters, for example, the luminance of a video signal may be controlled for one scene, the control reset to a starting position, and the control readjusted for a subsequent scene. Conventional control panels which employ potentiometers must manually be reset at the end of each operation to condition the control panel for a subsequent event. Needless to say, this is a tedious and time consuming activity.
One conventional control panel for a scene by scene color corrector which employs conventional rotary potentiometers avoids manual resetting. U.S. Pat. No. 4,096,523 to Belmares-Sarabia et al. discloses a control system where electromechanical means are employed to reset the control potentiometers quickly to a zero or null position in preparation for another color correction. The control potentiometers are adapted to be moved from a starting position to vary the magnitude of a color component or other control parameter. Electromagnetic positioning devices are used to reset the potentiometers to the zero or null position at the start of the next color correction, during the vertical video interval.
Another device for use in control panels which avoids manual resetting with pure electronic means is shown in U.S. Pat. No. 4,597,006 to Orsburn. In this patent, an optical position encoder mounted to the control panel provides control signals indicative of a desired increase or decrease in a controlled parameter as the operator turns a knob coupled to the shaft of the encoder. Circuitry responsive to the control signals accumulate the net increase or decrease in the controlled parameter in a memory location associated with a particular parameter. In particular, no physical movement or resetting of the encoders is required in the system shown in this patent in order to condition the control panel to accept changes for a subsequent event.
In order for the operator to monitor the amount of control being provided in the Orsburn system, a visual display on a computer monitor or on a numerical display LED or luminescent panel is provided as a control is turned. While this system conveniently allows repetitive corrections to be made without forcing tedious and repetitive manual resetting of the control knobs, the optical position encoders do not provide any position reference to the operator other than via the visual display. Although it is convenient for the operator to always begin a correction from the zero or null position, in some control situations the operator knows prior to actuating a control that significant amounts of control are desirable requiring the knob to be rotated several turns in order to approach the amount of control desired.
While the Orsburn system is certainly preferable to the electromechanical approach shown in the Belmares-Sarabia patent, there is a need for a control device wherein the operator can immediately approach the amount of control indicated virtually instantaneously and without having to turn a knob and watch a visual display. Accordingly, there is a need for a control apparatus which allows virtually instantaneous approach to the amount of control desired by an operator, while still providing the ability for instantaneous resetting to a null or zero position, for use in a computer controlled operator control panel.